How often are the lymphocytes produced

Function: What is the function of the various components of the immune system?

Author: Prof. Dr. med. Volker Wahn, Julia Dobke, Prof. Dr. med. Tim Niehues, editor: Ingrid Grüneberg, last changed: 29.05.2020

The immune system consists of various components that together ensure a functioning defense against disease. Since a primary immune defect can already be caused by the lack of individual components of the immune system, the tasks of the individual components of the immune system are explained below.

The tasks of white blood cells (leukocytes)

The leukocytes include the lymphocytes (B lymphocytes, T lymphocytes), granulocytes (neutrophils, eosinophils and basophils), monocytes (monocytes, macrophages, mast cells) and the natural killer cells (NK cells). Granulocytes, monocytes and NK cells are also known as phagocytes because they can ingest (phagocyte) and destroy pathogens or tumor cells directly.

The tasks of the B lymphocytes

The main task of the B cells is to produce a large amount of antibodies after they have matured into so-called plasma cells. Antibodies are y-shaped proteins that can specifically adhere to pathogens or foreign cells and, through their attachment, mediate their destruction. To a small extent, B lymphocytes can also control the immune system.

The most important antibodies (also called immunoglobulins) are:

  • The immunoglobulin A (IgA), which occurs on all mucous membranes and fights pathogens there.
  • The immunoglobulin G (IgG), the most common immunoglobulin. It is especially important to combat multiple infections. After first contact with a new pathogen, it takes about 3 weeks before it is functional. However, if the same infection occurs again, IgG antibodies are produced very quickly and in very large quantities in order to prevent the disease from breaking out again.
  • The immunoglobulin M (IgM), which is produced immediately when pathogens enter the body. It takes over the first fight against pathogens and is replaced by IgG, the specialized antibody, in the course of an infection.
  • The immunoglobulin E (IGE), which plays a role specifically in the defense against worm infections and in allergic reactions. It is only found in very small amounts in the blood.

The tasks of the T lymphocytes

T-lymphocytes go through a maturation phase in a certain, relatively small organ in the chest area, the thymus gland. In this phase the T-lymphocytes learn to recognize foreign or changed substances such as pathogens or changed (mutated) endogenous cells.

T cells can still change their receptors throughout their life in such a way that they can remember pathogens; this is called memory T cells.

T cells are able to control the entire immune system. They interact directly with other cells or send numerous different messenger substances into the immune system (so-called cytokines). In this way, they can activate other components of the immune system, such as the B cells.

The importance of T cells in the body is made clear by the fact that if they are missing, serious illnesses occur. A severe deficiency of T cells is fatal because sooner or later the most severe infections occur with pathogens that are rather harmless for healthy people.

T cells are also the cause of autoimmune diseases, which means that T cells turn against antigens on the body's own cells - so-called autoreactive T cells. Normally, T cells that have been mistakenly imprinted in the thymus gland for the body's own antigens should be destroyed in the thymus or at the latest after leaving the thymus gland, because they were incorrectly "programmed". If that doesn't work, autoimmune reactions can occur.

The tasks of the monocytes (phagocytes)

Monocytes belong to the unspecific immune defense. They are already present in the newborn. They are made in the bone marrow.

Monocytes have the task of absorbing material foreign to the body (phagocytizing) and rendering it harmless. To do this, however, they have to mature further and develop into macrophages. This does not happen in the bloodstream, but in the liver and connective tissue. Macrophages are then the actual phagocytes.

The tasks of the granulocytes

Granulocytes are also part of the unspecific immune defense. Granulocytes stay either on the inner walls of the vessels or in the circulating blood. They stay there for about seven hours and are then dismantled. They can move on their own and are able to migrate out of the blood vessels into the tissue and into the mucous membranes. After four to five days, the tissue-permeable granulocytes are also broken down.

Neutrophils specialize in defending against bacteria, viruses and fungi in the blood; eosinophil granulocytes help ward off parasites and are involved in allergic reactions; basophil granulocytes can also render parasites harmless and are involved in the occurrence of allergic reactions.

The tasks of the natural killer cells

Natural killer cells are part of the innate immune system and are a subgroup of lymphocytes. They are one of the first lines of defense in the fight against infection and cancer. For example, they form important messenger substances and can kill degenerate and infected cells such as pathogens or tumor cells.

The function of the complement system

The complement system belongs to the innate, unspecific immune defense. This system includes a large number of proteins that can recognize pathogens and other substances as foreign and “mark” them. Now the immune cells of the unspecific defense (granulocytes and phagocytes) can recognize the intruders and destroy them. The proteins of the complement system are also able to destroy the antigen-antibody complexes circulating in the bloodstream (lysis). The complement system can cause inflammation in the tissue to remove foreign bodies from the bloodstream more quickly.

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